Heat dissipation is a problem many electronic devices have to resolve. For instances, in personal computers, notebook computers and the like, overheated environments affect the performance and reliability of these electronic devices. Many machine malfunctions can be traced to heat-dissipating problems.
For example, in a computer system, the mother board has a central processing unit (CPU) for processing data operation. The CPU generates heat during operation and results in increasing temperature. When the temperature reaches a certain level, the CPU overheats and becomes unstable or even breaks down. The CPU is the main heat source of a computer system. To reduce the operation temperature of the CPU, a common practice is to install a heat sink on the CPU and place a fan on the heat sink so that the heat generated from the CPU is transmitted to the heat sink and the fan generates air flow to dissipate heat accumulated in the heat sink. In recent years, to meet the increasing demand of high-speed data processing, the manufacturing and design of CPUs have greatly improved. With improved performance and faster speed, operating voltages and frequencies for CPUs also increase. As a result, the CPU operation temperature becomes much higher. To meet a certain heat-dissipating requirements, it is necessary to enhance the heat-dissipating performance of fans.
Please refer to FIG. 1 showing a conventional fan. The fan 60 consists of a rotor 61 and a stator 62. The stator 62 is disposed in a frame 63 of the fan and telescoped outside a bearing tube 631. The rotor 61 has a shaft 611 and a plurality of blades 612. The blades 612 may generate airflow flowing toward the heat source. There is a pair of bearings disposed in the bearing tube 631 to couple with the shaft 611. When the fan has increased its operational efficiency, operation temperature of the fan also increases (when the fan is energized, permanent magnets in the fan are excited by the stator and the rotor is driven to rotate and generate heat resulting from friction between the bearing and the shaft). The fan operating in high temperature environments tends to have a lower durability. Furthermore, bearings are prone to be damaged when operation temperature exceeds a certain level. Damaged bearings impact fan's operation and also create noise.
Although fans are mainly used to dissipate the heat of external heat sources, they also generate heat and incur high operation temperature themselves under the requirement of high-efficiency operation. This phenomenon affects their useful life. With increasing performance demands of electronic products, this problem becomes more serious.